Aluminium powders with a mean particle size of around 1 µm were compacted by cold isostatic pressing (CIP) and additional forging.
The specimens are characterized by hot compression tests, dilatometry and metallography. A 3D interconnected structure of alumina films <5 nm in thickness is observed by transmission electron microscopy and field emission gun scanning electron microscopy; it is associated with the natural oxide skin which covers every aluminium powder and occupies around 3 vol.%. The compression tests are carried out in the range of 350-520 °C at strain rates of 0.003-3 s-1. The compressive strength was 100-150 and 130-180 MPa for the CIPed and forged samples, respectively. The low strain rate sensitivity m (<0.08) suggests that the alumina network forms a barrier, which suppresses any restoration mechanism across the grain boundaries as well as grain boundary sliding during hot deformation. The high strength of such compacted sub-micron Al powder is attributed to the conservation of a 3D alumina closed cell network filled with elastoplastic aluminium.